Abstract

An experimental effort to characterize the low Reynolds number flow‐induced self‐noise on a spherically shaped inertial sensor operating underwater is described. The transducer is a small geophone encased in a sphere, 76.2 mm in diameter. The sphere itself is cast from a 4:1 by volume of polystyrene microballons and epoxy resin, which yields a slightly negatively buoyant bluff body that is capable of sensing weak fluctuations in velocity such as those resulting from acoustic disturbances. When such a sensor is used in ocean environments, a spurious self‐noise signal oftentimes exists due to low velocitycurrents. The research described in this paper quantifies this flow‐induced noise signal as a function of the sphere diameter Reynolds number (0<Red<20 000) and it is found that the broadband (10 to 1000 Hz) flow‐induced signal is due to the turbulent flow structures shed by the sphere. Virtually no broadband noise is produced when the Reynolds number is subcritical and the shed vortices are laminar. [Work supported by Naval Air Warfare Center, Warminster, PA under ONR contract.]